M. Di Martino, Turin Astronomical Observatory,
I-10025 Pino Torinese (TO), Italy.
G. Longo, INFN and University Physics Department,
via Irnerio 46, I-40126 Bologna, Italy.
The expedition will carry out a systematic exploration around the site (101° 53' 40'' E; 60° 53' 09'' N) of the so-called Tunguska event. The main goal is to assess the real nature of the body that on June 30, 1908 devastated about 2,000 km² of Siberian taiga felling more than 60 million of trees. Following the eyewitness's testimony, a cosmic fireball sailed over about 1000 km of Siberian territory leaving a trail of light some 800 km long. Subsequent researches showed that the Tunguska bolide exploded at an altitude of about 8 km emitting an energy equivalent to 10-50 Megatons of TNT. No macroscopic remnants of the body, neither the typical signature of an impact, like a crater, have been found by the expeditions that previously visited the region. Nevertheless, it is the most devastating cosmic body known to strike Earth in historic times.
On July 1996, in Bologna, an international conference, attended by about 100 scientists (astronomers, physicists, chemists, biologists, geologists, etc.), discussed the various aspects of the event (see abstracts). Many questions are still open and an well-organised expedition with precise tasks will help to give an answer about the nature and composition of the Tunguska Cosmic Body. This will be a valuable contribution to the international programs on the detection and physical study of asteroids and comets potentially dangerous to humankind.
The fundamental tasks of the "Tunguska99" expedition are:
1. the study of Ceko lacustrine sediments,
2. magnetometric measurements, and radar and photographic observations,
3. the search for cosmic body fragments, fallen before the explosion, and of tree samples,
4. cosmic-ray measurements during the flight Bologna-Tunguska-Bologna and in Tunguska.
2. A topographic survey of the area will be performed using a GPS system in order to re-examine the aerophotographic material, obtained in 1938 under the direction of L.A. Kulik. The comparison between the 1938 pictures and the new survey should give further information on the direction of the trees felled by the explosion. Moreover, this comparison will make it possible to evaluate the changes of the environmental conditions and will provide a contribution to the research program of the "Tunguska Natural Reserve". The presence of magnetic anomalies that previous ground investigations have attributed to the collisional event will also be verified.
3. Some theories presented in 1996 at the Bologna conference on Tunguska presume that, before the explosion of the cosmic body, some macroscopic fragments fell in the south-east area with respect to the epicentre. Supposing that the cosmic body was chondritic, thus containing a high percentage of iron-nickel, the separation of fragments from ground rocks can be performed using neodymium magnets mounted on a special device together with a metal detector (Hall effect probe). This perfectly working system has been tested with good results during two expeditions in the western Egyptian desert and is available at the Physics Department of the Bologna University. Moreover, more samples of the trees surviving the explosion will be collected, in order to further the investigation carried out by the first Italian expedition.
4. The proposed expedition will also make it possible to measure cosmic rays with the high efficiency radiation detectors, already used by the Bologna group in Italy, Antarctica, Arctica, Everest valley (5000 m) and along the entire sea trip Ravenna-Antarctica-Ravenna. These detectors will be used to monitor cosmic rays, both during the flight Bologna-Tunguska-Bologna and during the two-week stay in the Tunguska Natural Reserve. Gamma rays from cosmic radiation will be continuously recorded on time scale of one minute and in the 0.05-3 Mev, 3-5 Mev and 5-20 Mev energy bands. The comparison between previous measurements and those in flight and on the ground will allow the study of cosmic ray variations with altitude, longitude, pressure, temperature, humidity, and solar activity.
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